 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui.internal;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.jface.action.IAction;
 import org.eclipse.ui.IPageListener;
 import org.eclipse.ui.IPerspectiveDescriptor;
 import org.eclipse.ui.IWorkbenchPage;
 import org.eclipse.ui.IWorkbenchWindow;
 import org.eclipse.ui.PerspectiveAdapter;

 /**
  * Utility class for tracking the active perspective in a window.
  *
  * @since 3.1
  */
 public class PerspectiveTracker extends PerspectiveAdapter implements
         IPageListener {

     private IWorkbenchWindow window;

     private IAction action;

     /**
      * Creates a perspective tracker for the given window.
      * Subclasses should override <code>update(IPerspectiveDescriptor)</code>
      * to get notified of perspective changes.
      *
      * @param window the window to track
      */
     protected PerspectiveTracker(IWorkbenchWindow window) {
         Assert.isNotNull(window);
         this.window = window;
         window.addPageListener(this);
         window.addPerspectiveListener(this);
     }

     /**
      * Creates a perspective tracker for the given window which will
      * enable the given action only when there is an active perspective.
      *
      * @param window the window to track
      * @param action the action to enable or disable
      */
     public PerspectiveTracker(IWorkbenchWindow window, IAction action) {
         this(window);
         this.action = action;
         update();
     }

     /**
      * Disposes the tracker.
      */
     public void dispose() {
         if (window != null) {
             window.removePageListener(this);
             window.removePerspectiveListener(this);
         }
     }

     public void pageActivated(IWorkbenchPage page) {
         update();
     }

     public void pageClosed(IWorkbenchPage page) {
         update();
     }

     public void pageOpened(IWorkbenchPage page) {
         // ignore
 }

     public void perspectiveActivated(IWorkbenchPage page,
             IPerspectiveDescriptor perspective) {
         update();
     }

     /**
      * Determines the active perspective in the window
      * and calls <code>update(IPerspectiveDescriptor)</code>.
      */
     private void update() {
         if (window != null) {
             IPerspectiveDescriptor persp = null;
             IWorkbenchPage page = window.getActivePage();
             if (page != null) {
                 persp = page.getPerspective();
             }
             update(persp);
         }
     }

     /**
      * Performs some function based on the active perspective in the window.
      * <p>
      * The default implementation enables the action (if given) if there
      * is an active perspective, otherwise it disables it.
      * </p>
      * <p>
      * Subclasses may override or extend.
      * </p>
      *
      * @param persp the active perspective in the window, or <code>null</code> if none
      */
     protected void update(IPerspectiveDescriptor persp) {
         if (action != null) {
             action.setEnabled(persp != null);
         }
     }

 }

